System and method for the removal of particulates from water

ABSTRACT

An underwater system ( 1 ) has a hydrocylone ( 5 ) for separating sand from seawater, and a pump ( 8 ) downstream from the hydrocylone ( 5 ) for drawing seawater upstream of the hydrocylone into the hydrocylone. The sand separated from the seawater is collected in a sand storage device ( 6 ) below the hydrocyclone. The pump ( 8 ) pumps the seawater from which the sand has been removed into a water injection well ( 16 ) and a portion of the seawater is diverted into a sand extraction device ( 7 ) beneath the sand storage device ( 6 ) to flush away the sand collected therein.

The present invention relates to the removal of particulates from water,particularly in situations when seawater is to be used for injectioninto a hydrocarbon reservoir.

In an oil and/or gas field development, production fluid, extracted fromthe hydrocarbon reservoir via production wells, is normally driven to ahost facility by the natural pressure of the reservoir. However, thenatural pressure varies from field to field and some reservoirs,particularly in later field life, may not have enough natural pressureto drive the production fluid to the host facility.

A way of overcoming this problem is to boost the pressure of thereservoir by injecting seawater, via water injection wells, into thereservoir at a pressure higher than the pressure of the fluid in thereservoir. Where this has been done previously, seawater is pumped fromthe sea up to a host facility such as a floating platform where it istreated so as to make it suitable for injection into the hydrocarbonreservoir. Such treatment may include both the use of chemicals andparticulate removal in a settlement tank to allow suspended sediment tosettle and be separated from the seawater. If such sediment is notremoved it will cause abrasive wear in equipment and pipelines that theseawater passes through and may adversely affect production from thehydrocarbon reservoir. The substantially sediment free seawater is thenpumped from the settlement tank at high pressure down to the waterinjection wells and into the reservoir.

Pipelines are required to convey the treated water from the hostfacility to the injection wells and these pipelines have to have a pipewall thick enough to withstand the high internal pressure of the treatedseawater. The capital costs of such pipelines and the installation costsare high.

Thus, the process for injecting seawater into injection wells, requiresseawater to be pumped up to a host facility where it is suitably treatedbefore being pumped at high pressure into the wells. This processinvolves expensive equipment such as high pressure pipelines and pumps.Furthermore, the large amount of energy required to pump the seawaterover a long distance from the host facility to the injection wells willincrease the running costs.

An object of the invention is to overcome at least some of the problemsreferred to above.

Thus, according to one aspect of the present invention there is provideda system for use underwater for removing particulates from water,comprising dynamic separating means for removing particulates fromwater, and pumping means downstream from the dynamic separating meansfor drawing water upstream of the separating means into the separatingmeans.

The pumping means may be used to inject at least substantiallyparticulate free water from the dynamic separating means into ahydrocarbon reservoir at a pressure higher than the pressure of thefluid in the reservoir.

By providing such a system underwater, the length of high pressurepipelines required between the pumping means and injection wells can bemuch less than when treated seawater is to be pumped from a hostfacility. A pump is not required upstream of the separating means topump water into the separating means (as in the prior art arrangementexplained above) and the abrasion problem associated with pumpingparticulate laden seawater is thereby avoided.

The dynamic separating means may comprise at least one dynamicseparator. Such separators are simple, compact, self-contained unitswhich are suitable for use underwater. The dynamic separating means maycomprise one or more hydrocyclones.

The system may be provided with means for collecting particulatesseparated from said water by the dynamic separating means and means forremoving collected particulates from the particulate collecting means.The particulate removal means may continuously remove collectedparticulates or periodically remove collected particulates. Preferably,the system includes means for directing at least some of the at leastsubstantially particulate free water from the dynamic separating meansto the particulate removal means to enable the particulate removal meansto remove collected particulates. The particulate removal means maycomprise a venturi flume.

The system may have a filter upstream of the dynamic separating meansfor preventing large items such as fish from entering the separatingmeans.

Preferably, the system is incorporated into a retrievable module for usewith a modular seabed processing system.

According to another aspect of the present invention there is providedan underwater method for removing particulates from water, comprisingthe steps of pumping water downstream of dynamic separating means todraw water upstream of the separating means into the separating means,and separating particulates from the water in the dynamic separatingmeans.

The method preferably includes the subsequent step of injecting at leastsubstantially particulate free water from the dynamic separating meansinto a hydrocarbon reservoir at a pressure higher than the pressure ofthe fluid in the reservoir.

The invention will now be described, by way of example only, withreference to the accompanying drawings, in which:

FIG. 1 schematically shows a system in accordance with an embodiment ofthe present invention;

FIG. 2 is a schematic detail of the inside of a module for the system ofFIG. 1;

FIG. 3 is a modification of FIG. 2; and

FIG. 4 is a modification of FIG. 3.

Referring to FIGS. 1 and 2 of the accompanying drawings, the system 1 isaccommodated in a retrievable module 2 which is connected to a basestructure 3 on a seabed by a multi-ported fluid connector 4 for enablingisolation of the module 2 from the base structure 3. The module 2 may beof the general type forming part of a modular system for subsea usedesigned by Alpha Thames Limited of Essex, United Kingdom, and referredto as AlphaPRIME.

The module 2 contains a sand or particulate or particle removal device5, a sand storage vessel 6, a dynamic sand extraction device 7, and apump 8. The sand removal device 5 is a dynamic separator and may be ahydrocyclone separator of the type produced by Axsia Mozley of Redruth,Cornwall, United Kingdom. The sand removal device 5 has a fluid inlet 9,a fluid outlet 10 and a sand or particle outlet 11. The fluid inlet 9 isconnected via a fluid inlet conduit 12 to a coarse filter 13 located onan outside face of the module 2, and the fluid outlet 10 is connected tothe multi-ported fluid connector 4 by a fluid outlet conduit 14containing the pump 8. The fluid outlet conduit 14 is connected to aconduit 15 leading to one or more water injection wells (indicated byarrow 16) via the multi-ported fluid connector 4 and each conduit 14,15includes an isolation valve 17 on either side of the fluid connector 4.

The sand outlet 11 of the sand removal device 5 is connected to a sandinlet 18 of the sand storage vessel 6 below via an actuable isolationvalve 19. The vessel 6 has a sand outlet 20 which is connected to thesand extraction device 7 below by a flange connection 21.

The dynamic sand extraction device 7 is connected by a bypass conduit 22to the fluid outlet conduit 14 downstream of the pump 8 and the bypassconduit 22 has a flow and pressure restriction device 23 and an actuableisolation valve 24 downstream of the device 23. The bypass conduit 22 isconnected to a side 25 of the sand extraction device 7 and a sandremoval conduit 26 extends through the base 27 of the device 7 and upinto the lower portion 28 of the sand storage vessel 6 via the flangeconnection 21. The sand removal conduit 26 extends in the oppositedirection to connect to a port 29 on the side of the module 2, and hasan actuable isolation valve 30 between the sand extraction device 7 andthe port 29.

The operation of the system 1 will now be described.

The isolation valve 19 between the sand removal device 5 and the sandstorage device 6 is set to be open and the isolation valves 24,30 oneither side of the sand extraction device 7 are set to be closed. Thepump 8 in the module 2 is activated to draw raw seawater into the sandremoval device 5 via the coarse filter 13. The flow induced by the pump8 results in a helical flow being established in the device 5 whichleads to the separation of sand and other particulates from theseawater. The sand removal device 5 removes sand and other particulatesfrom the seawater, and the separated sand is collected in the lowerportion of the sand storage device 6 therebelow. The pump 8 pumps theseawater separated from the sand via the fluid outlet 10 and themulti-ported fluid connector 4 into the water injection well(s).

Periodically, the sand storage device 6 is flushed. The isolation valve19 between the sand removal device 5 and the sand storage device 6 isclosed and the isolation valves 24,30 on either side of the sandextraction device 7 are opened. A portion of the seawater in the fluidoutlet conduit 14 is carried by the bypass conduit 22 into the sandextraction device 7 which causes it to swirl into the lower portion ofthe sand storage device 6 and flush collected sand into the sand removalconduit 26 and out into the surrounding sea via the port 29.

FIG. 3 illustrates a modification of the system 1 whereby the sandremoval device 5 and the sand storage device 6 are replaced by acombined sand removal and storage device 31.

In FIG. 4, the sand removal and storage device 31 is connected to anejector 32 instead of a sand extraction device 7, and the isolationvalves 24,30, which were either side of the sand extraction device 7,are removed. The ejector 32 is a venturi flume and the bypass conduit 22is connected to the inlet end of it and an outlet conduit 33 connectsthe other end of it to the module port (not shown). The waist of theventuri flume 32 is connected to the sand outlet 34 of the sand removaland storage device 31 by a sand outlet conduit 35.

The modified system of FIG. 4 is designed to flush sand continuouslyfrom the sand removal and storage device 6. Flow of seawater from thebypass conduit 22 through the ejector 32 draws sand down from the sandremoval and storage device 6 and the sand and seawater are ejected intothe surrounding sea via the port 29.

Whilst embodiments have been described, it will be understood thatvarious modifications may be made without departing from the scope ofthe invention. For example, for any of the above arrangements theconduit 26,33 to the port 29 may have a one-way valve to preventseawater surrounding the module 2 from being sucked into the module 2.

The arrangement for removing collected sand illustrated in FIG. 3 may bedesigned to continuously take separated sand away by removing theisolation valves 24,30 on either side of the sand extraction device 7.

For the above described embodiments, the multi-ported fluid connector 4may be replaced by a fluid connector with a single bore.

1. An underwater hydrocarbon reservoir water injection system forremoving particulates from water, comprising: separating means forremoving particulates from water; and pumping means downstream from saidseparating means for drawing surrounding water upstream of saidseparating means into said separating means; wherein said system isincorporated into a retrievable module for use with a modular seabedprocessing system; wherein said separating means comprises dynamicseparating means comprising a hydrocyclone; and wherein said systemfurther comprises means for collecting particulates separated from saidwater by said dynamic separating means, means for removing collectedparticulates from said particulate collecting means and means fordirecting at least some of the at least substantially particulate freewater from said dynamic separating means to said particulate removalmeans to enable said particulate removal means to remove collectedparticulates and eject them into water surrounding the module.
 2. Thesystem as claimed in claim 1, wherein said pumping means is arranged toinject at least substantially particulate free water from said dynamicseparating means into a hydrocarbon reservoir at a pressure higher thanthe pressure of fluid in said reservoir.
 3. The system as claimed inclaim 1, including a combined dynamic separating and particulatecollecting means.
 4. The system as claimed in claim 1, wherein saidparticulate removal means is arranged to periodically remove collectedparticulates.
 5. The system as claimed in claim 1, wherein saidparticulate removal means is arranged to continuously remove collectedparticulates.
 6. The system as claimed in claim 1, wherein theparticulate removal means comprises a venturi flume.
 7. The system asclaimed in claim 1, comprising a filter upstream of said dynamicseparating means.
 8. An underwater method for removing particulates fromwater and injecting the resulting water into a hydrocarbon reservoir,comprising the steps of: pumping water downstream of separating means todraw surrounding water upstream of the separating means into theseparating means; and separating particulates from the water in theseparating means and injecting the resulting water into a hydrocarbonreservoir; wherein the separation occurs in a retrievable module for usewith a modular seabed processing system, the particulates are separatedfrom the water in dynamic separating means comprising a hydrocyclone andcollected in a collecting means, then removed from the collecting meansby particulate removal means to which at least some substantiallyparticulate free water from the dynamic separating means is directed toenable the particulate removal means to remove collected particulatesand eject them into water surrounding the module.
 9. The method asclaimed in claim 8, including the subsequent step of injecting at leastsubstantially particulate free water from the dynamic separating meansinto a hydrocarbon reservoir at a pressure higher than the pressure offluid in the reservoir.